Abstract
The purpose of this study was to evaluate the performance and refine the design of the collimation system for the gamma radiation source (GBS) currently being realised at ELI-NP facility. The gamma beam, produced by inverse Compton scattering, will provide a tunable average energy in the range between 0.2 and 20MeV, an energy bandwidth 0.5% and a flux of about 108photons/s. As a result of the inverse Compton interaction, the energy of the emitted radiation is related to the emission angle, it is maximum in the backscattering direction and decreases as the angle increase [1,2]. Therefore, the required energy bandwidth can be obtained only by developing a specific collimation system of the gamma beam, i.e. filtering out the radiation emitted at larger angles. The angular acceptance of the collimation for ELI-NP-GBS must be continuously adjustable in a range from about 700 to 60μrad, to obtain the required parameters in the entire energy range. The solution identified is a stack of adjustable slits, arranged with a relative rotation around the beam axis to obtain an hole with an approximately circular shape. In this contribution, the final collimation design and its performance evaluated by carrying out a series of detailed Geant4 simulations both of the high-energy and the low-energy beamline are presented.
Highlights
ELI-NP is one of the three pillars of the ELI (Extreme Light Infrastructures) European Project, currently under realisation in Bucharest, Romania. This facility will host the Gamma Beam System (GBS), an intense and monochromatic gamma beam source based on Inverse Compton (IC) interaction between a high-power laser and an accelerated electron beam produced by a warm LINAC
The gamma beam generated by IC interactions is not intrinsically monochromatic and the photon energy is related to the emission angle [1,2]
The choice of making 3 group of 4 slits with the same rotation around the beam axis was taken because from the simulation resulted that this configuration, together with the 2 additional slits position at the end of the stacks, guarantees less spurious events in the HPGe detector of the Compton spectrometer [4]
Summary
ELI-NP is one of the three pillars of the ELI (Extreme Light Infrastructures) European Project, currently under realisation in Bucharest, Romania. This facility will host the Gamma Beam System (GBS), an intense and monochromatic gamma beam source based on Inverse Compton (IC) interaction between a high-power laser and an accelerated electron beam produced by a warm LINAC. The gamma beam is expected to feature an energy ranging from 0.2 to 20 MeV, a 0.5% energy bandwidth and a flux of about 108 photons/s Such photon source will be devoted to the investigation of a broad range of applications, from nuclear physics and astrophysics, to material and life sciences. The photons emitted along the electron beam axis feature the maximum energy, which in a first
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